Several extensions of the Standard Model predict the production of dark matter particles at the LHC. An uncharted signature of dark matter particles produced in association with VV=W±Wa"or ZZ pairs from a decay of a dark Higgs boson s is searched for using 139 fb-1 of pp collisions recorded by the ATLAS detector at a center-of-mass energy of 13 TeV. The s→V(qq)V(qq) decays are reconstructed with a novel technique aimed at resolving the dense topology from boosted VV pairs using jets in the calorimeter and tracking information. Dark Higgs scenarios with ms>160 GeV are excluded.